Study On The Temperature Stability Of All Fiber Optical Current Transformer

Electrical energy is one of the most important energy sources in our lives,so the transmission and detection of electrical energy is also of great significance.Compared with the traditional electromagnetic current transformer,the Fiber Optical Current Transformer has the advantages of anti-electromagnetic interference,no magnetic circuit saturation,no open circuit risk,good stability and high precision,and has the advantage that the traditional transformer can't match in the DC measurement.Therefore,the Fiber Optical Current Transformer becomes a hot topic.However,the main problem with the current all-fiber current sensor is that the longterm stability is not good.The accuracy of the sensor measurement will be reduced due to environmental influences such as temperature changes.The problems that arise are mainly in two aspects: First,the precision devices such as phase modulators,light sources,and photodetectors aged during working,which result in a decrease in system sensing accuracy.Second,the sensing unit is exposed in a harsh environment for a long time,so changes in temperature and other factors can affect the transmission characteristics of the ?/4 wave plate and the sensing fiber in the sensing unit,thus affecting the accuracy of the measurement.In this paper,wo discussed about the solution to improve the temperature stability of the system by studying on the temperature characteristics of the sensing unit.The main work of this paper includes the following:(1)The Jones matrix model of the Fiber Optical Current Transformer based on Faraday rotation effect is established,and the relationship between the output signal of the system and the key parameters of each component in the system is analyzed.Then we studied how the devices such as light source and polarization and the PM fiber fusion angles affect the output signal of the system.(2)Fiber Optical Current Transformer system under open-loop conditions is implemented.Firstly,the principle of system modulation and demodulation is introduced theoretically.The simulation signal of the detection signal,the demodulation process and the recovered signal are obtained by simulating the process of modulation and demodulation.And the self-coherence demodulation algorithm and its feasibility is verified,too.Then introduced the selection of the devices such as light source,polarizer,birefringence phase modulator,photodetector and others from the hardware aspect.Finally,the temperature cycling experiment for detecting the performance of the sensing unit is introduced.A batch of sensing units were tested,and the range of the relative error was 1.4% in the range of-40 ? to 70 ?.(3)We studied the effects of the temperature characteristics of Verdet constant and ?/4 wave plate on the system and the compensation between them by using Jones matrix model.Taking the problems that may occur in actual production into consideration,we proposed and experimentally proved that the wave plate of 1/4 beat length can be replaced by the wave plate of 3/4 beat length.The manufacturing process of ?/4 wave plate and the packaging process of the sensing coil are introduced.And we tested the performance of the wave plate in the range of-40? to 70 ? to found that the relative error was decreased from 1.4% to about 0.6% without applying temperature compensation algorithm.